One technique to establish thermal equilibrium and to achieve a controlled heat removal rate is taught by SE 350,606 and comprises immersing the sampling vessel in a molten bath of the metal to be analyzed or heating the vessel in some other way, in order to establish thermal equilibrium between the sampling vessel and its contents at a temperature above the temperature of crystallisation prior to commencement of the cooling process of the thermal analysis. A sampling vessel adapted for this technique is also disclosed, that vessel being made of graphite, for use in aluminium melts, or made of a ceramic material, when intended for use in melt cast iron.
Another sampling vessel for thermal analysis, though only directed at aluminium alloys, is disclosed in DK-B-150,996. That vessel comprises a small crucible of steel sheet, provided with a plug of thermally insulating material, e.g. core sand, at the bottom.
Apart from the vessels mentioned above, there are several other sample vessels of the similar kind occuring in the art. A common drawback for these vessels is that they all are made of, or comprise as an essential part, materials such as graphite, furan sand, core sand or refractory cement; these materials are all known to be difficult to work. The available manufacturing techniques are slow and have considerable quality problems due to the nature of the material. Although it would be desirable to provide for various vessel features, giving a variety of different heat removal characteristics, in order to produce sampling vessels adapted for thermal analysis of different metals and alloys, this has hitherto not been possible, since the limited choice of materials for producing such vessels has seriously restricted the latitude to select among these characteristics. Likewise, it has been difficult to provide sampling vessels that give cooling rates that are sufficiently accurate and repeatable to fulfil the requirements of thermal analysis, due to the constricted selection of characteristics obtainable.
Regarding the sampling vessels of immersion type, i.e. the ones that are immersed in the bulk of the melt metal when sampling, a special drawback is the risk of thermal shock cracking, particularly when the vessels are made of ceramic materials. Sampling vessels made according to prior art of course also suffer from the risk of contamination the molten metal sample.